The chemical behavior for Mo(0) and W(0) complexes, [M(CO)$_2$(PPh$_3$)$_4$] (M=Mo and W),has been investigated by UV-vis spectroscopic, magnetic, and electrochemical methods. Three absorption bands are observed in the UV-spectra. The crystal-field-splitti ng energy, spin-pairing energy, and bond strengths were deduced from the spectra. The metal d electrons in both complexes seemed to be delocalized in low-spin state.Metal ligand correlation appeared to strongly depend on bond strengths and diamagnetic properties. In electrochemical processes, both complexes exhibit an irreversible reduction wave.